The present invention relates to a terminal land frame, which substitutes for a conventional leadframe with radial leads and includes lands functioning as external terminals, and also relates to a method for manufacturing the same.
In recent years, to catch up with rapidly advancing downsizing of electronic units, it has become increasingly necessary to assemble semiconductor components, like resin-molded semiconductor devices, at a higher and higher density. Correspondingly, sizes and thicknesses of semiconductor components have also been noticeably reduced. In parallel with this downsizing trend, the number of pins required for a single electronic unit is also increasing day after day. To meet these demands, resin-molded semiconductor devices of a greatly reduced size and with a drastically reduced thickness should now be assembled at an even higher density.
Hereinafter, a conventional leadframe for a resin-molded semiconductor device will be described.
FIG. 24 is a plan view illustrating the structure of a conventional leadframe. As shown in FIG. 24, the conventional leadframe includes: a rectangular die pad 102; support leads 103; radial inner leads 104; outer leads 105; and tie bars 106, all of these members being provided inside a frame rail 101. The die pad 102 is used for mounting a semiconductor chip thereon. The support leads 103 support the die pad 102. The inner leads 104 are electrically connected to the semiconductor chip mounted with some connection means like metal fine wires. The outer leads 105 are joined to the respective inner leads 104 and to be connected to external terminals. The tie bars 106 are provided for joining and fixing the outer leads 105 together and for preventing the overflow of a resin encapsulant during a resin molding process.
It should be noted that an ordinary leadframe does not consist of a single pattern such as that shown in FIG. 24, but is made up of a plurality of such patterns, which are arranged to be connected together both horizontally and vertically.
Next, a conventional resin-molded semiconductor device will be described. FIG. 25 is a cross-sectional view illustrating a resin-molded semiconductor device using the leadframe shown in FIG. 24.
As shown in FIG. 25, a semiconductor chip 107 is mounted on the die pad 102 of the leadframe. The semiconductor chip 107 is electrically connected to the inner leads 104 via metal fine wires 108. The semiconductor chip 107 on the die pad 102 and the inner leads 104 are encapsulated with a resin encapsulant 109. The outer leads 105 protrude from the sides of the resin encapsulant 109 and the ends thereof are bent downward.
Next, a method for manufacturing the conventional resin-molded semiconductor device will be described with reference to FIG. 26. First, the semiconductor chip 107 is bonded, with an adhesive, onto the die pad 102 of the leadframe. This process step is called “die bonding”. Next, the semiconductor chip 107 is connected to the respective ends of the inner leads 104 via the metal fine wires 108. This process step is called “wire bonding”. Subsequently, the semiconductor chip 107 and a portion of the leadframe inside the tie bars 106 (i.e., the inner leads 104 and so on) are molded with the resin encapsulant 109 such that the outer leads 105 protrude outward. This process step is called “resin molding”. Finally, portions slightly inside the tie bars 106 are cut off to separate the outer leads 105 from each other and remove the frame rail 101, and the respective ends of the outer leads 105 are bent. This process step is called “tie bar cutting and bending”. As a result, a resin-molded semiconductor device with the structure shown in FIG. 25 is completed. In FIG. 26, a region surrounded by the dashed line is to be molded with the resin encapsulant 109.
As described above, the number of devices that should be integrated within a single semiconductor chip, or the number of pins per chip, has been on the rise these days. In other words, the number of outer leads should also be increased to catch up with the latest trend. That is to say, the number of the inner leads, which are joined to the outer leads, should preferably be increased to cope with such an implementation. However, the width of the inner (or outer) lead has a processable limit. Thus, as the number of inner leads is increased, the overall size of the leadframe and that of the resulting resin-molded semiconductor device also increase. That is to say, it is difficult to realize a downsized and thinned resin-molded semiconductor device in such a case. On the other hand, if only the number of inner leads is increased to cope with the rise in number of pins of a semiconductor chip while using a leadframe of substantially the same size, then the width of a single inner lead should be further reduced. In such a case, it becomes more difficult to perform various process steps for forming the leadframe, like etching, as originally designed.
Recently, semi-face-mount semiconductor devices, such as ball grid array (BGA) types and land grid array (LGA) types, are also provided. A semiconductor device of such a type is mounted directly on a motherboard on the bottom. Specifically, first, a semiconductor chip is mounted on a carrier (i.e., a printed wiring board) including external electrodes on the bottom thereof. Next, the semiconductor chip is electrically connected to the external electrodes. And then the chip is molded with a resin on the upper surface of the carrier. The semiconductor devices of this face-mount type, which is mounted directly on a motherboard on the bottom, will be mainstream products in the near future. Accordingly, it is now clear that the conventional leadframe and resin-molded semiconductor device using the leadframe will soon be out of date under the circumstances such as these.
Also, the conventional resin-molded semiconductor device includes outer leads protruding outward from the sides of a resin encapsulant, and is supposed to be mounted onto a motherboard by bonding the outer leads to the electrodes of the motherboard. Accordingly, the conventional device cannot be mounted onto the board so reliably as the semiconductor devices of BGA and LGA types. Nevertheless, the semiconductor devices of the BGA and LGA types are more expensive, because these devices use a printed wiring board. That is to say, it is difficult for any of these conventional types of semiconductor devices to attain high reliability at a low cost.